In 1996 a workshop on Measurement of Oxidative Stress in Humans was held at NIEHS. There was a general consensus that it would be valuable to mount a study comparing various markers of oxidative stress measured from the same sample. One such marker is F2a-isoprostane which is quantitated by NICI-MS. The mass spectrometry workgroup has agreed to undertake these analyses within NIEHS. We have since elaborated the analytical scheme to improve overall yield and reliability of the sample workup protocol, and are currently determining isoprostane levels in the round-robin study. A number of other studies involving measurement of isoprostanes as an indicator of oxidative stress have also been initiated. One such study is a collaboration with NCI (Dr. Phil Taylor) and USDA (Drs. David Baer and Joseph Judd) as part of the Women's Alcohol Study. The aim of the part of the study we are participating in is to determine the effect of alcohol consumption on lipid levels, oxidative stress, and micronutrient levels in postmenopausal women, and to assess the influence of alcohol and hormone metabolism genetic polymorphism on hormone levels. A second study probes questions raised by recent prevention and intervention trials that implied that consumption of carotenoid-rich foods early in disease states provides a protective advantage while late intervention with dietary carotenoids exacerbates cancer. It is hypothesized that an anti- oxidant environment only during the earliest stage of tumorigenesis will ultimately decrease the incidence and severity of tumors; conversely, the same anti-oxidant regimens fed after appearance of preneoplastic foci will lead to exacerbation of the subsequent tumor burden. We will provide quantitative measurement of oxidative stress in these studies which include both animal and cell culture studies.